Polylactic acid resins have been expected as bio-polymers which can serve as substitutes for resins produced from fossil raw materials such as petroleum because a monomer lactic acid can be inexpensively produced from a biomass raw material such as maize by a fermentation method utilizing a microorganism, and its melting point is also as high as about 170° C. so that melt-molding can be carried out.
However, polylactic acid resins have a slow crystallization velocity, thereby posing limitations on their use as molded articles. For example, in a case where a polylactic acid resin is injection-molded, there are serious practical disadvantages in moldability and heat resistance that not only a long molding cycle time and heat treatment after the molding are necessitated, but also deformation upon molding or upon heat treatment is large.
On the other hand, the techniques of blending plural resins have been widely known as polymer-alloy techniques, which are widely utilized for the purposes of improving the disadvantages of the individual polymers.
Patent Publication 1 discloses a thermoplastic resin composition having widely improved mechanical properties, hydrolytic resistance, and heat resistance by combining a polylactic acid resin and an aromatic polyester resin.
Patent Publication 2 discloses an automobile part made of a polylactic acid resin composition having excellent heat resistance, obtained by blending a polylactic acid resin with a separately prepared specified propylene resin composition, and further including glass fiber, a modified propylene resin, and a crystallization promoter thereto.
Patent Publication 3 discloses a resin composition having excellent moldability, impact resistance, and heat resistance, by blending a polylactic acid resin, and a polyolefin resin, and a specified compatibilizing agent.
In addition, Patent Publication 4 discloses a resin composition containing a polyolefin, a polylactic acid and a carboxylic acid ester of a polyhydric alcohol, wherein the polylactic acid and the carboxylic acid ester of a polyhydric alcohol are blended in specified amounts, whereby a resin composition is provided with mechanical properties, such as tensile modulus and tear strength, that are sufficient for practical purposes. More specifically, Example 1 gives an example of a film obtained by kneading a polylactic acid and a carboxylic acid ester of a polyhydric alcohol to form a polylactic acid master batch, blending the resulting master batch with a polyethylene, and molding the mixture to form a film.